#include <stdio.h>
#include <math.h>

int main()
{
    int i, count;
    printf("There are invertable primes with 4 digits:\n");
    for (count = 0, i = 1001; i < 9999; i += 2)
        if (num(i))
            printf(count % 9 ? "%3d:%3d" : "%3d:%d\n", ++count, i);
}
num(int number)
{
    int j, i;
    if (!ok(number))
        return (0);
    for (i = number, j = 0; i > 0; i /= 10)
        j = j * 10 + i % 10;
    if (number < j)
        if (!ok(j))
            return (0);
        else
            return (1);
    else
        return (0);
}
ok(int number)
{
    int i, j;
    if (number % 2 == 0)
        return (0);
    j = sqrt((double)number) + 1;
    for (i = 3; i <= j; i += 2)
        if (number % i == 0)
            return (0);
    return (1);
}